How to determine if an object is an instance of certain derived C++ class from a pointer to a base class in GDB?

c++ types gdb superclass instanceof
user1101096 picture user1101096 · Dec 16, 2011 · Viewed 20k times · Source

I'm debugging a C++ program with GDB.

I have a pointer to an object of certain class. The pointer is declared to be of some super class which is extended by several sub-classes.

There is no fields in the object to specify the precise class type of this object but some virtual functions (e.g. bool is_xxx()) are defined to tell the class type at runtime.

Is there some way to tell the precise class type of an object in GDB without calling these virtual functions. Calling such functions in GDB may generate confusing result when the program is multi-threaded.

Answer

Beta picture Beta · Dec 16, 2011

Use ptype. If you use it by itself, you get the declared type of the pointer:

(gdb) ptype ptr
type = class SuperClass {
  // various members
} *

To get the actual type of the object pointed to, set the "print object" variable:

(gdb) set print object on
(gdb) ptype ptr
type = /* real type = DerivedClass * */
class SuperClass {
  // various members
} *

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